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Study: Metformin May Lower Lung Cancer Risk in Diabetic Nonsmokers

Authors report ‘unexpected’ finding

Among nonsmokers who had diabetes, those who received the diabetes drug metformin had a decrease in lung cancer risk, according to a new study published in Cancer Prevention Research, a journal of the American Association for Cancer Research.

“Metformin use was not associated with lung cancer risk when we looked at all patients with diabetes. However, our results suggest that the risk might differ by smoking history, with metformin decreasing risk among nonsmokers and increasing risk among current smokers,” said Lori C. Sakoda, PhD, MPH, a research scientist at the Kaiser Permanente Division of Research in Oakland, California.

“Our results suggesting that the risk associated with metformin might differ by smoking history were unexpected,” added Sakoda. “Additional large, well-conducted studies are needed to clarify whether metformin may be used to prevent lung or other cancers, particularly in specific subpopulations, such as nonsmokers.”

Some laboratory studies and a number of observational studies have suggested that metformin may prevent cancer, but the data from human studies are conflicting, Sakoda explained. The researchers conducted the new investigation to further clarify the association between the use of metformin and lung cancer risk.

Sakoda and colleagues conducted a retrospective cohort study of 47,351 diabetes patients (54% men), aged 40 years or older, who completed a health-related survey between 1994 and 1996. Information regarding their diabetes medications was collected from electronic pharmacy records. Approximately 46% of the subjects were “ever-users” of metformin, defined as those who filled two or more prescriptions within a 6-month period.

During 15 years of follow-up, 747 patients were diagnosed with lung cancer. Of these individuals, 203 (27%) were current smokers and 80 (11%) were never smokers.

The use of metformin was not associated with lower lung cancer risk overall; however, the risk was 43% lower among diabetes patients who had never smoked, and the risk appeared to decrease with longer use of the drug, according to the authors. Nonsmokers who used metformin for 5 years or longer had a 52% reduction in lung cancer risk, but this finding was not statistically significant.

Moreover, metformin use for 5 or more years was associated with a 31% decrease in the risk for adenocarcinoma, the most common type of lung cancer diagnosed in nonsmokers, and an 82% increase in the risk for small-cell carcinoma, a type of lung cancer often diagnosed in smokers, but, again, neither of these findings was statistically significant.

The study was funded by the National Institutes of Health.

Source: AACR; February 2, 2015.

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